Acute myocardial infarction is one of the leading causes of death in the developed world and is fast becoming a leading cause of death even in the developing world. If a patient has access to a hospital with interventionalists on 24 hr a day call, the chances of opening an infarct-related artery (IRA) within 90-120 minutes of the onset of chest pain is 85%. Most patients, even in the US, do not have access to such facilities and if they arrive at a regional hospital are likely to receive thrombolytic therapy that has a success rate of 60% in opening the infarct-related artery. If some other non-invasive and easily applied treatment could enhance the success of thrombolytics alone and bring it closer to the 85% that can be achieved with percutaneous coronary interventions, it could have a major public health impact. The overall aim of this proposal is to develop novel ultrasound device technologies for microbubble-ultrasound mediated treatment of acute myocardial infarction. The specific aims of this proposal are to develop an integrated in vivo therapy-imaging system to: 1. Determine the optimal ultrasound parameters that cause successful thrombolysis in vivo using a vascular shunt model in baboons. 2. Develop therapy probe(s) that can deliver appropriate ultrasound energy to the thrombus in order to dissolve it and reduce microthromboembolism after reperfusion. 3. Integrate the therapy probe(s) with a 4D ultrasound imaging system that can image microbubbles in vivo and gate ultrasound pulses to automatically dissolve the thrombus. 4. Determine the mechanisms of myocardial microcirculation during acute coronary occlusion and prevent microthromboembolism after reperfusion by treating the myocardium with ultrasound. This proposal is for a Biomedical Research Parternership that involves the leaders in the country in their specific fields. Steve Hanson, PhD (OHSU) is an expert on thrombosis and has used innovative baboon models to study thrombolysis. Thomas Porter, MD (University of Nebraska) is a pioneer in the use of microbubbles and ultrasound for arterial thrombus dissolution. Robert Siegel, MD (Cedars-Sinai, UCLA) has described the novel findings of direct myocardial protection by ultrasound during acute coronary occlusion that is independent of its effect on the thrombus. Sanjiv Kaul, MD, (OHSU) has pioneered the field of MCE and has developed sophisticated techniques to assess the microcirculation, including measurement of no reflow, quantifying regional myocardial perfusion, and molecular imaging. Pierre Khuri-Yakub (Stanford) is a leader in transducer technology, and GE is a world leader in ultrasound systems. Xubo Song (OHSU) is an authority on deterministic tracking algorithms that can assist in delivery of ultrasound to the correct target in a beating heart.